1. Field of the Invention
The present invention relates to zoom lens systems suitable for cameras such as video cameras, silver-halide-film cameras, broadcast cameras, and digital still cameras, and to image pickup apparatuses including the same.
2. Description of the Related Art
Recent image pickup apparatuses, such as video cameras, digital still cameras, broadcast cameras, and silver-halide-film still cameras, that include solid-state image pickup devices have higher functions and are of smaller sizes.
Image taking optical systems included in such image pickup apparatuses are desired to be compact lens systems with a short total length and a high zoom ratio and to exhibit good optical performance at all zoom positions.
For example, Japanese Patent Laid-Open No. 3-296706 and U.S. Pat. Nos. 6,975,461 and 6,853,496 disclose compact four-group zoom lens systems that have a high zoom ratio and perform zooming by moving individual lens groups provided with refractive powers of positive, negative, positive, and positive in that order from the object side to the image side.
Additionally, U.S. Pat. Nos. 6,069,743 and 6,577,450 disclose four-group zoom lens systems each of which includes a second lens group consisting of a pair of a negative lens element and a positive lens element.
In general, a zoom lens system that includes lens groups each including a larger number of lens elements has a long optical axis for each of the lens groups.
Moreover, a zoom lens system that includes lens groups that move large distances during zooming and focusing has a long total length.
When the refractive power of each lens group is increased to reduce the size of the zoom lens system, the moving distance of each lens group during zooming is reduced, whereby the total length can be reduced. However, a simple increase of the refractive power of the lens group increases changes in aberrations during zooming. It is difficult to compensate for such aberrations in a good manner.
That is, to simultaneously achieve compactness, a high zoom ratio, and good optical performance of an optical system, it is important to appropriately set the moving conditions during zooming, refractive powers, and configurations of individual lens groups.